[actions] Support Semgrep by Github Actions (#40)

Signed-off-by: maipbui <maibui@microsoft.com>
#### Why I did it
[Semgrep](https://github.com/returntocorp/semgrep) is a static analysis tool to find security vulnerabilities.
When opening a PR or commtting to PR, Semgrep performs a diff-aware scanning, which scans changed files in PRs.
When merging PR, Semgrep performs a full scan on master branch and report all findings.
Ref: - [Supported Language](https://semgrep.dev/docs/supported-languages/#language-maturity) - [Semgrep Rules](https://registry.semgrep.dev/rule)
#### How I did it
Integrate Semgrep into this repository by committing a job configuration file
#### How to verify it
PR: maipbui/sonic-buildimage#2
Master branch full scan findings: [Master branch findings results](https://github.com/maipbui/sonic-buildimage/actions/runs/3160181876/jobs/5144332404)
PR maipbui/sonic-buildimage#2 scan findings: [Pull request findings results](https://github.com/maipbui/sonic-buildimage/actions/runs/3160193505/jobs/5144357859)

.github/workflows/semgrep.yml

@@ -0,0 +1,21 @@
+name: Semgrep
+
+on:
+  pull_request: {}
+  push:
+    branches:
+      - master
+      - '201[7-9][0-1][0-9]'
+      - '202[0-9][0-1][0-9]'
+
+jobs:
+  semgrep:
+    name: Semgrep
+    runs-on: ubuntu-latest
+    container:
+      image: returntocorp/semgrep
+    steps:
+      - uses: actions/checkout@v3
+      - run: semgrep ci
+        env:
+           SEMGREP_RULES: p/default